Geology of Gemstones


There is no generally accepted definition for the term gemstone.  But gemstones almost always have some special characteristic about them.  Most are beautiful, some are worn as status symbols, some are religious and some are even believed to have medicinal powers. **

Most gemstones are minerals or mineral aggregates.  They can be rocks, organic formations or even synthetic.

Since most gemstones are minerals it is the origin and structure that concerns the geologist when classifying a stone.


Origin: There are several ways minerals can be formed into gemstones.  Some can crystalize from molten magma from the earth’s interior,  others from lava flows on the exterior.  There are those the crystalize from hydrous solutions and some the from with the help of organisms near the earth’s surface.

Structure:  There are seven types of crystal systems:  Cubic, tetragonal, Hexagonal (or trigonal) orthorhombic, monoclinic, triclinic.  Refers to Schumann’s book for examples.





Notes of Gemstone Names


Ametrine:  Ametrine is a two colored quartz.  Its contains varying amounts of violet amethyst and yellow-brown citrine.  The primary source of Ametine is from Bolivia.

Moonstone or Blue Moonstone:  This name is actually a false name but is widely used.  The actual stone is chalcedony that has been artificially blue tinted.  It gives the stone a blue hue that changes with the angle of light which that makes it look like it is “glowing”.  We have some pieces on our site made with these stones.




**Source: Gemstones of the World, 5th edition, Walter Schumann